Gasification of solid carbonaceous fuel



July 2, 1968 HEBDEN ET AL GASIFICATION OF SOL ID CARBONACEOUS FUEL Filed Jan. 27, 1964 m H x fi M w e I M m A wk 5 M United States Patent 3,390,971 GASIFICATION OF SOLID CARBONACEOUS FUEL Dennis Hebden, Solihull, and John Aldwyn Lacey, Dorridge, Solihull, England, assignors to The Gas Council, London, England, a British statutory corporation Filed Jan. 27, 1964, Ser. No. 340,219 Claims priority, application Great Britain, Jan. 31, 1963,

6 Claims. (Cl. 4863) ABSTRACT OF THE DISCLOSURE In the gasification of a bed of ash-containing solid carbonaceous fuel in the shaft of a gasifier by introducing gasifying agent into the bed through a plurality of tuyeres distributed around the lower part of the shaft, the uniformity of distribution of the gasifying agent over the cross-section of the shaft is improved by supplying the gasifying agent from some tuyeres at a velocity giving central gasification and from the remaining tuyeres at a velocity giving peripheral gasification, and periodically changing the velocity from each tuyere from one of said velocities to the other so as to avoid a preponderance of either central or peripheral gasification.

This invention relates to the operation of gasifiers of the kind having a shaft in which a static bed of an ashcontaining solid carbonaceous fuel, such as coal or coke, is gasified, advantageously under superatmospheric pressure, by means of a gasifying agent that is introduced into the lower part of the fuel bed from a plurality of tuyeres distributed round the lower part of the inner wall of the shaft of the gasifier, the gasification is carried out at a high temperature such that the-ash collects beneath the fuel bed in a liquid form, fresh fuel is continuously supplied to the bed, and the liquid ash is continuously discharged from the lower part of the gasifier. The word continuously is used herein to include both the uninterrupted and the intermittent supply of fuel or discharge of liquid ash.

The tuyeres may be water-cooled, and may project a short distance into the fuel bed from the inner wall of the gasifier, which wall may be of refractory material or be water-cooled. The gasifying agent may be a mixture of steam and/or carbon dioxide with oxygen or air enriched with oxygen. The velocity at which the gasifying agent issues from the tuyeres determines the extent to which it penetrates into the fuel bed. It is difficult to establish a velocity such that the gasifying agent is distributed sufiiciently uniformly over the cross-sectional area of the shaft of the gasifier, since the limits of velocity are relatively close. Moreover, working within these limits would undesirably restrict variation in the throughput of the gasifier. When the velocity is below these limits there is poor penetration of the bed and gasification occurs preferentially in the outer region of the bed adjacent to the inner wall of the shaft (hereinafter referred to as peripheral gasification) and liquid ash may solidify on cooled tuyeres to interfere with the flow of gasifying agent. When the velocity is above these limits gasification occurs preferentially in the central region of the bed (hereinafter referred to as central gasification), and there may be formed in front of one or more of the tuyeres a void or region deficient in combustible material in which liquid ash can come into contact with the relatively cool gasifying agent and be chilled and solidified, which interferes with the flow and distribution of the gasifying agent.

An object of the present invention is to improve the 3,390,971 Patented July 2, 1968 distribution of the gasifying agent over the cross-sectional area of the gasifier shaft and avoid the aforesaid disadvantages.

The invention provides a method of operating a gasifier of the kind described above, wherein the gasifying agent is caused simultaneously to issue from some of the tuyeres at a velocity that would give preferential central gasification and from the remaining tuyeres at a velocity that would give preferential peripheral gasification, and the velocity from each tuyere is periodically changed from one of the aforesaid velocities to the other in such manner that a preponderance of either central or peripheral gasification and interference with the flow of the gasifying agent due to the solidification of ash in the vicinity of the tuyeres are avoided, and that each change causes no alteration in the rate of supply of the gasifying agent from all the tuyeres collectively.

Since the velocity of the gasifying agent issuing from a tuyere is directly proportional to the rate at which gasifying agent is supplied thereby, that is to say, the quantity supplied in unit time, the velocity can be controlled by controlling the quantity of gasifying agent supplied in unit time.

In order that each periodical change from one velocity to the other shall cause no alteration in the overall rate of supply of gasifying agent from all the tuyeres, the ratio of the number of tuyeres operating at one velocity to the number of tuyeres operating at the other velocity should be the same before and after each change. However, during the gasification the overall rate of supply of gasifying agent from all the tuyeres may be varied by varying the total quantity of gasifying agent supplied to them, although it is usual, at least for a given period, to maintain the total quantity constant to ensure a continuous and unvarying output from the gasifier.

A simple and advantageous method of carrying out the change in velocity is to operate a group consisting of one half of the tuyeres at one velocity and a group consisting of the other half of the tuyeres at the other velocity, and to change each group simultaneously from operation at one velocity to operation at the other velocity. The tuyeres that are to constitute each group are advantageously so selected that each tuyere belonging to one group has adjacent to it on each side a tuyere belonging to the other group. The maximum period during which the two groups of tuyeres are operated at their respective velocities must not result in the development of a preponderance of either central gasification or peripheral gasification, or in interference with the flow of the gasifying agent due to the solidification of ash in the vicinity of the tuyeres.

The maximum length of the intervals at which the change-over from one velocity to the other should be made, in order to avoid interference with the flow of gasifying agent due to the solidification of ash in the vicinity of the tuyeres, depends on the rate of formation of ash, which depends primarily on the ash content of the carbonaceous fuel and the throughput of the gasifier. The higher the ash content and the higher the throughput the shorter is the maximum length of the intervals, and vice versa. In general the maximum length of these intervals is within the range of from 15 seconds to 5 minutes.

The invention also provides a gasifier suitable for carrying out the method of operation described above, which comprises a plurality of tuyeres distributed round the lower part of the inner wall of the shaft of the gasifier, supply means for causing gasifying agent to issue simultaneously from some of the tuyeres at one rate and from the remaining tuyeres at a different rate, valve means for changing the rate from each tuyere from one of the rates to the other, and timing means for periodically operating the said valve means at predetermined intervals.

The gasifier advantageously comprises supply means for causing gasifying agent to issue simultaneously from a group consisting of one half of the tuyeres at one rate and from a group consisting of the other half of the tuyeres at a different rate, and valve means for changing each group simultaneously from operation at one rate to operation at the other rate. For this purpose the supply means may comprise a main supply conduit, two conduit systems for supplying gasifying agent from the main supply conduit at substantially the same rate to the two groups of the tuyeres, a supplementary conduit system for supplying additional gasifying agent from the main supply conduit to each group of tuyeres, and valve means operable so as to connect the supplementary conduit system alternatively to one or the other group of tuyeres.

The term gasification is used herein to include any reaction between a solid carbonaceous fuel and a gas (hereinbefore referred to as the gasifying agent) to produce from the carbonaceous material of the fuel one or more gases, that is to say, products that are in the gaseous state under atmospheric pressure and temperature, for example, carbon monoxide, hydrogen, carbon dioxide, methane or ethane. The gasifying agent may be, for example, oxygen or air alone or in admixture with steam and/or carbon dioxide, or it may be hydrogen.

The gasification may be carried out under atmospheric pressure, but superatmospheric pressure is preferable when it is desired to increase the rate of throughput.

The method of the invention and a gasifier suitable for carrying it out are exemplified with reference to the accompanying drawings, in which FIGURE 1 shows in vertical cross section the lower part of the gasifier and the associated valve control means in diagrammatic form, and

FIGURE 2 is a horizontal cross section taken on the line 22 in FIGURE 1.

The gasifier has an outer casing 1 lined with a refractory material 2. The hearth 3 has a discharge outlet 4 for liquid ash. Six tuyeres, of which three are indicated by the reference numeral 5 and the other three by the reference numeral 6, are arranged at equal distances apart and so as to project into the shaft of the gasifier above the region in which liquid ash collects. The three tuyeres 5 are supplied with gasifying agent from a circular pipe 7 that surrounds the gasifier externally, and the tuyeres 6 are supplied with gasifying agent from a similar pipe 8. The pipes 7 and 8 are supplied with gasifying agent from a main supply pipe 9 leading to three branch pipes 10, 11 and 12. The branch pipes and 12 communicate with the circular pipes 7 and 8, respectively. The branch pipe 11 leads to a change-over valve 13, which, in one position as shown in FIGURE 2, puts the pipe 11 into communication with a pipe 14 leading to the circular pipe 7 and out of communication with a pipe leading to the circular pipe 8. When rotated clockwise through 90 degrees, the valve 13 puts the pipe 11 into communication with the pipe 15 and out of communication with the pipe 14.

The rate at which gasifying agent is supplied through the pipes 10 and 12 to the pipes 7 and 8, respectively, is substantially the same, and the rate at which gasifying agent is supplied alternately to the circular pipes 7 and 8 from the pipe 11 through the pipes 14 and 15, respectively, is adjusted so as to change the rates supplied alternately to the circular pipes between the limits required at each change of velocities. Thus, for example, if the velocity required for preferential central gasification were three times that required for preferential peripheral gasification, 1 volume of gasifying agent would be supplied in unit time through each of the pipes 10 and 12, and 2 volumes would be supplied through the pipe 11, so that the rate of supply to each circular pipe would alternate from 3 volumes to 1 volume and vice versa, and the total rate of supply of 4 volumes would remain constant at each change of velocities. The change-over valve 13 is operated automatically by a timing device (not shown).

In each of the branch pipes 10, 12 and 11 there is shown a nozzle or orifice plate 16, which fixes the rate of supply of gasifying agent through the pipes 10 and 12 and through the pipe 14 or 15,-' respectively, and which causes a pressure drop sufliciently high to remain substantially unchanged by the periodical changes in pressure in the circular pipes 7 and 8 that occur when the valve 13 is operated. In order to enable the ratio of the supply rates to the pipes 7 and 8 to be varied there may be provided across the nozzle or orifice plate 16 in the pipe 11 a device for measuring the pressure drop across it and an adjustable valve in the pipe 11 upstream of the nozzle or orifice plate 16. Alternatively, each of the nozzles or orifice plates 16 in the pipes 10 and 12 may also be provided with a pressure drop measuring device and an adjustable valve upstream thereof, so that the rates of flow in those pipes can be separately adjusted to be the same.

The operation of the valve 13 may be controlled automatically so as to be changed from one position to the other at predetermined intervals by timing means of known type, for example, a pair of electrically controlled time switches which operate alternately to move the valve 13 from one position to the other, maintain the valve in the latter position for a predetermined period for which the switch is set, and at the end of that period to energise the other switch to repeat the cycle of operations.

The fuel may be continuously supplied to the gasifier, and the molten ash continuously discharged therefrom, in known :manner. For example, when the gasification is carried out under superatmospheric pressure, the fuel may be supplied to the gasifier through a lock hopper communicating with an inlet in the top of the shaft, and the molten ash may be similarly discharged through a lock hopper communicating with the discharge outlet 4.

The following example illustrates the method of the invention:

In a gasifier of the kind shown in the accompanying drawing, and of which the shaft had an internal diameter of 7 feet 6 inches, a coal having an ash content of 10 percent by weight and a particle size of 0.5 to 1 inch was gasified under a pressure of 20 atmospheres with a gasifying agent consisting of a mixture of 1.2 parts by volume of steam and 1 part by volume of oxygen. The coal was supplied to the gasifier at the rate of 18 tons per hour, and the gasifying agent was supplied through the six tuyeres at the rate of 440,000 cubic feet per hour. A part of the gasifying agent was supplied at therate of 110,000 cubic feet per hour through the pipe 10 to the circular pipe 7 and at the same rate through the pipe 12 to the circular pipe 8. The remainder of the gasifying agent was supplied at the rate of 220,000 cubic feet per hour through the pipe 11 and via the valve 13 alternately through the pipe 14 to the circular pipe 7 and through the pipe 15 to the circular pipe 8. Thus, in one position of the valve 13 (as shown in the drawing) the gasifying agent was supplied to the group of three tuyeres 5 at the rate of 330,000 cubic feet per hour and to the group of three tuyeres 6 .at the rate of 110,000 cubic feet per hour. In the other position of the valve 13 these rates of supply to the two groups of tuyeres were reversed. The gasifying agent issued at a velocity of 270 feet per second from the tuyeres operating at the higher'of these supply rates and at a velocity of feet per second from the tuyeres operating at the lower of these supply rates. At the higher and lower velocities the gasifying agent penetrated approximately 44 inches and 20 inches, respectively, into the fuel beds. The valve 13 was changed from one position to the other at intervals of2 minutes. The maximum temperature in the fuel bed was about 1800" C. The rate of gas production was 1,000,000 cubic feet per hour, and the gas produced (calculatd as dry gas) had the following composition:

Percent by vol. Carbon dioxide 3.0 Unsaturated hydrocarbons 0.2 Carbon monoxide 60.0 Hydrogen 27.3 Methane 8.5 Nitrogen 1.0

We claim:

1. A method of operating a gasifier having a shaft in which a static bed of an ash-containing solid carbonaceous fuel is gasified by introducing a gasifying agent in the lower part of the fuel bed from a plurality of tuyeres distribute-d around the lower part of the inner wall of the shaft, the gasification being carried out at a high temperature such that the ash collects in liquid form beneath the fuel bed, fresh fuel being continuously supplied to the bed, and the liquid ash being continuously discharged from the lower part of the gasifier, wherein the gasifying agent is caused simultaneously to issue from some of the tuyeres at a velocity that would give preferential central gasification and from the remaining tuyeres at a velocity that would give preferential peripheral gasification, and the velocity from each tuyere is periodically changed from one of the aforesaid velocities to the other in such manner that a preponderance of either central or peripheral gasification and interference with the flow of the gasifying agent due to the solidification of ash in the vicinity of the tuyeres are avoided, and that the ratio of the number of tuyeres operating at one of the said velocities to the number of tuyeres operating at the other of the said velocities is the same before and after each change.

2. A method as claimed in claim 1, wherein a group consisting of one half of the tuyeres is operated at one of the said velocities and a group consisting of the other half of the tuyeres is operated at the other velocity, and each group of tuyeres is changed simultaneously from operation at one velocity to operation at the other velocity.

3. A method as claimed in claim 2, wherein each tuyere belonging to one group of tuyeres has adjacent to it on each side a tuyere belonging to the other group of tuyeres.

4. A gasifier, which comprises a shaft to contain a static bed of ash-containing solid carbonaceous fuel, a plurality of tuyeres distributed around the lower part of the inner wall of the shaft of the gasifier, supply means for causing gasifying agent to issue simultaneously from some of the tuyeres at one rate and from the remaining tuyeres at a different rate, valve means for changing the rate from each tuyere from one of the rates to the other, and timing means for periodically operating the said valve means at predetermined intervals.

5. A gasifier as claimed in claim 4, wherein the supply means causes gasifying agent to issue simultaneously from a group consisting of one half of the tuyeres at one rate and from a group consisting of the other half of the tuyeres at a different rate, and valve means for changing each group simultaneously from operation at one rate to operation at the other rate.

6. A gasifier as claimed in claim 5, wherein the supply means comprises a main supply conduit, two conduit systems for supplying gasifying agent from the main supply conduit at substantially the same rate to the two groups of tuyeres, a supplementary conduit system for supplying additional gasifying agent from the main supply conduit to each group of tuyeres, and valve means operable so as to connect the supplementary conduit system alternately to each of the two groups of tuyeres.

References Cited UNITED STATES PATENTS 1,098,534 2/1914 Servais 48-206 1,896,799 2/1933 Loebell 48-73 X 2,175,610 10/1939 Linder 48-206 X 2,594,468 4/ 1952 MacKenzie et a1 48206 JOSEPH SCOVRONEK, Primary Examiner. 

